1. Field of the Invention
The present invention relates to a semiconductor memory device. For example, the present invention relates to the arrangement of a voltage generator that generates a boosted voltage to be used inside a semiconductor memory device.
2. Description of the Related Art
Conventional nonvolatile semiconductor memories use a boosted voltage obtained by boosting an external voltage. A voltage generator that generates this boosted voltage normally includes a plurality of charge pump circuits in order to ensure the boosting ability of the voltage generator (e.g., patent reference 1).
In the conventional voltage generator, however, a large electric current sometimes flows through a plurality of charge pump circuits because the charge pump circuits are sometimes simultaneously turned on depending on the state of a control signal that controls the charge pump circuits or the control signal itself is unstable. This electric current produces noise and causes a data read error. This problem is particularly serious when a read operation and one of a write operation and erase operation are simultaneously performed across different memory blocks (this operation is called a dual operation).
[Patent reference 1] Jpn. Pat. Appln. KOKAI Publication No. 2000-331489